Key matrix circuit

Details Key matrix circuit Key matrix circuit

2000-08-03

2003-01-21

Horabik, Michael (Department: 2635)

Coded data generation or conversion

Bodily actuated code generator

Including keyboard or keypad

C341S020000, C341S022000, C340S014100

Reexamination Certificate

active

06509846

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a key matrix circuit used in radio equipment or the like, and more particularly it relates to a circuit configuration with a minimized number of input circuits to a microcomputer circuit for recognition of selected keys, and to an associated keyboard and circuit board construction.
2. Description of the Related Art
In the past, a keyboard in which selection and setting keys are arranged in a matrix was applied to the operating panel of a transceiver or the like.
FIG. 9
shows a circuit diagram of such a keyboard, which has a 4-by-4 matrix of keys enabling selection of hexadecimal values from 0 to f.
With this key matrix circuit, there are lines
101
for the circuits
1
to
4
corresponding to the keys in the X direction (row direction), lines
102
for the circuits
5
to
8
corresponding to the keys in the Y direction (column direction), and selection keys
103
at intersections between these circuits.
The lines
101
for circuits
1
to
4
are each connected to a power supply Vcc via a resistance Rx
1
to Rx
4
, respectively, and the lines
102
for circuits
5
to
8
are each connected to ground via a resistance Ry
5
to Ry
8
, respectively.
Therefore, when an arbitrary selection key is set t on, a p line in the X direction and a q line in the Y direction which intersect at the key are connected, a voltage (Vd) that is divided from the power supply voltage Vcc by the resistance Rxp and Ryq is output to each circuit. The lines
101
for circuits
1
to
4
and the lines
102
for circuits
5
to
8
are connected to input ports of a microcomputer circuit, which, based on the event of the voltage on the X-direction p line and the Y-direction q line becoming the voltage Vd, recognizes which key of the 16 selection keys has been pressed, in response to which a control command or the like corresponding to the selected key is output.
Another method is the singular method shown in FIG.
10
.
As shown in
FIG. 10
, this is the simplest system, in which if there are 16 selection keys, an on/off signal from each of the selection keys KEY
1
to KEY
16
is individually output to an input port of a microcomputer circuit, which monitors the state of each input port, and recognized therefrom which selection key has been pressed.
Yet another method is the A/D method shown in FIG.
11
.
In this circuit, if there are
16
selection keys, the power supply voltage Vcc is connected in series to the resistances R
1
to R
16
, and individual selection keys KEY
1
to KEY
16
are connected between the connection points between the resistances R
1
to R
16
and ground, and between the far end of resistance R
16
and ground, these keys being set to on and off, and the connection point between the resistances R
1
and R
2
being connected to an input port of a microcomputer circuit.
With the above-noted circuit arrangement, when a key KEYp is pressed, a voltage (Vd) that is the power supply voltage Vcc divided between resistance R
1
and the series resistance R
1
+R
2
+. . . +Rp) is output to the connection point between resistance R
1
and resistance R
2
, this voltage being A/D converted by the microcomputer circuit, so as to recognize which key has been pressed, in response to the converted voltage level.
In a multiple-key input system using, for example, a ten-key pad to make various data inputs and settings in a transceiver or the like, a microcomputer circuit is used, as noted above, to perform recognition of a selected key and output of a control command and data, because of a desire to reduce the number of wiring lines and reduce the cost of components, there is a desire to use a system with a reduced number of input circuits to the microcomputer circuit and a small number of ports.
It would appear that, in response to this need, using the A/D system shown in
FIG. 11
, in principle only one circuit is required for a large number of selection keys, the microcomputer circuit performing recognition of what key is pressed from the voltage level after A/D conversion.
However, the usual power supply voltage Vcc of a microcomputer circuit is 5 V, and the need to achieve stable discrimination of a divided voltage imposes a requirement that a threshold be set approximately every 1 V.
Thus, in reality even the A/D system shown in
FIG. 11
is limited to discrimination of five levels, or six levels if the open condition is added, so that it is not capable of discriminating the on/off states of 16 selection keys as shown in FIG.
11
.
Accordingly, it is an object of the present invention to provide a key matrix circuit configuration that reduces the number of signal circuit lines to a microcomputer that performs recognition of selection keys to the minimum number, while enabling stable recognition of selected keys. It is a further object of the present invention to provide a keyboard having a construction suited to the above-noted circuit configuration.
SUMMARY OF THE INVENTION
To achieve the above-noted objects, the present invention is a key matrix circuit, having a keyboard with a plurality of selection keys arranged in an N-row-by-M-column matrix, a board having switching circuits having a first terminal and a second terminal that are connected to a common ground circuit when a corresponding selection key is pressed, the first terminals of each switching circuit, corresponding to the selected key in the row direction being connected to a first connection circuit in units of rows, and the second terminals of each switching circuit, corresponding to the selected key in the column direction being connection to a second connection circuit in units of columns, an output circuit wherein a fixed-voltage power supply and one circuit of the first connection circuits are connected by a first voltage-dividing circuit formed by a series connection of N resistances, with other first connection circuits connected to points between the other resistances of the first voltage-dividing circuit, a first output point being a resistance connection point of the first connection circuit via one resistance from the fixed-voltage power supply, and wherein a fixed-voltage power supply and one circuit of the second connection circuits are connected by a second voltage-dividing circuit formed by a series connection of M resistances, with other second connection circuits connected to points between the other resistances of the second voltage-dividing circuit, a second output point being a resistance connection point of the second connection circuit via one resistance from the fixed-voltage power supply, and a microcomputer circuit which A/D converts and captures the voltages at the first output point and the second output point of the output circuit and, using a data table, into which are stored identification data and control commands corresponding to combinations of voltage levels that the first output point can take and voltage levels that the second output point can take, these combinations being related to each selection key, performs recognition of a pressed selection key and execution of corresponding control.
According to the present invention, when a selection key is pressed, voltages that are established by the row and column to which the key belongs are output to the first output point and the second output point.
More specifically, by a switching circuit corresponding to a pressed key changing to the on state, the grounded connection location first voltage-dividing circuit and second voltage-dividing circuit, which are series resistance circuits, is set by the row and column to which the pressed key belongs, in response to which the voltage division condition which respect to the fixed-voltage power supply voltage in each of the voltage-dividing circuits is established, each of these divided voltages appearing as outputs at the first output point and the second output point.
When the above occurs, because each of the voltage-dividing circuits is a series resistance circuit, each divided voltage differs, dependi

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